Because the safety to the human body is valued in the medical adhesive, it should be specifically considered to select the raw materials. For example, when an aromatic polyisocyanate, which does not contain a fluorine atom, is used as a polyisocyanate component, an unreacted aromatic polyisocyanate remaining in the urethane prepolymer reacts with water in the body fluid such as blood to turn into an aromatic amine which has high possibility of mutagenicity. Therefore, using the aromatic polyisocyanate as a raw material for the medical adhesive has a problem from the viewpoint of safety.
Moreover, when an aliphatic polyisocyanate or an alicyclic polyisocyanate is used as a polyisocyanate component, because the reactivity of an isocyanate group in the urethane prepolymer is low, there is a problem of not obtaining a practical curing rate at the temperature in the vicinity of the body temperature.
Then, as a medical adhesive with safety against mutagenicity etc. and practical reactivity (curing rate), a medical adhesive comprising a fluorine-containing hydrophilic urethane prepolymer terminated by an isocyanate group obtained by the reaction of a fluorine-containing polyisocyanate and a hydrophilic polyether polyol has been developed (Japanese Kokai Publication Hei-1-227762 (corresponding patent application: U.S. Pat. No. 4,994,542A, and the like), and International Publication WO03/051952 (corresponding patent application: A.U. Patent No. 2002343788A1, and the like)).
This medical adhesive comprising a fluorine-containing hydrophilic urethane prepolymer terminated by an isocyanate group reacts with water in the body fluid such as blood and lymph to form an amine and carbon dioxide, and this amine further reacts with the fluorine-containing hydrophilic urethane prepolymer terminated by an isocyanate group and promotes molecular weight-increasing process (polymerization), and the adherend can be bonded. At this time, the urethane prepolymer foams by the generated carbon dioxide and becomes a spongelike cured product (product cured by the reaction with water). And, this cured product (foam) is excellent in adhesive strength and flexibility.
A cured product (the foam product obtained by the reaction with water), which is obtained by curing a conventional medical adhesive, has such a problem as easily deteriorate and decompose with the passage of time and can not be said to be excellent in the duration of adhesive strength. For example, part or all of the cured product (foam sheet) obtained by applying this conventional medical adhesive (comprising the fluorine-containing hydrophilic urethane prepolymer terminated by an isocyanate group) on a glass board and soaking the board in water to cure the adhesive becomes viscous liquid (deteriorates/decomposes) on several days at 25 to 40° C., and the adhesive strength might decrease greatly.